Thin IC cards have been produced in such a procedure as follows. Electronic components are mounted, by using solder or the like, on lands of a wiring pattern formed on a first cover sheet which is made of vinyl chloride having good self-fusing characteristic. A core sheet made of vinyl chloride, having apertures at positions corresponding to the electronic components mounting positions, is placed over the electronic components. Space around the electronic components in the apertures is filled up with a sealing resin made of a thermosetting resin such as epoxy resin which is cured after filling. Then after placing a second cover sheet made of vinyl chloride on the sealing resin, the assembly of sheets is heated at about 120.degree. C. for 5 to 10 minutes while applying a pressure of 5 kgf/cm.sup.2 by means of a press, thereby completing the thin IC card.
The sealing resin is preferably applied so that the surface is at the same height as the core sheet surface, but the resin changes the volume thereof when curing, and therefore it is difficult to accurately control the amount of the resin to fill. Further, while portions other than the filling resin join with each other through thermal fusion of vinyl chloride, top surfaces of the filling resin are exposed through the cover sheet, resulting in a problem that clear image cannot be printed when printing a pattern on the cover sheet surface.
Thus, it is a first object of the present invention to provide a method for producing a thin IC card with beautiful finish of the cover sheet surface at positions corresponding to the apertures of the core sheet.
Vinyl chloride is capable of self-fusing at a low temperature and is suitable for mass production in a continuous production line. However, vinyl chloride emits a chloride gas when burned, thus polluting the environment. Recently, therefore, it has been proposed to switch the material from vinyl chloride to polyethylene terephthalate (PET). However, polyethylene terephthalate has a melting point above 250.degree. C. and is not self-fusing at a low temperature unlike vinyl chloride. Also in case a thermosetting resin is used as a filling resin of IC cards produced in the continuous production line, such a method cannot be employed as the apertures of the core sheet are filled with the thermosetting resin followed by a period of waiting for the thermosetting resin to cure during the production step. Instead, it is necessary to apply the thermosetting resin on the electronic components in advance. But this method has a problem of causing more impairment of the surface construction of the cover sheet than in the case of the former method.
Thus, it is a second object of the present invention to provide a method for mass producing a thin IC card by using PET which does not have adverse effect on the environment, in a similar way as that for vinyl chloride, while producing the thin IC card of beautiful surface finish.